In an adhesive material used for Flexible Printed Circuits (hereinafter, referred to as “FPC”), a mixture of an epoxy resin and a curing agent of the epoxy resin is contained as a curing component, and a nitrile-butadiene rubber (hereinafter, referred to as “NBR”) or the like is blended in order to improve separation strength of the adhesive material and impart flexibility to the adhesive material. As this NBR, a resin composition containing a carboxyl group capable of being cross-linked to an epoxy resin has been widely used in order to obtain good solder heat resistance (See PTL 1).
Since an adhesive composition used for FPC contains a large amount of an epoxy resin, a large amount of the epoxy resin and the like unreacted exudes at the time of hot-press forming, thereby causing a problem that a drilled portion provided in a cover lay, a reinforcing plate, or the like is plugged.
PTL 2 has proposed a method of preventing an adhesive composition from exuding from a drilled portion by allowing the adhesive composition to contain an ultraviolet (UV) curable resin and irradiating the drilled portion with ultraviolet rays to cure the ultraviolet curable resin.
However, in the technique disclosed in PTL 2, a step of UV irradiation is added, and therefore capital investment for the step of UV irradiation and a special storage condition for avoiding ultraviolet rays during storage are required.